Prolongation of antibiotic prophylaxis after clean and clean-contaminated surgery and surgical site infection

AIM

Several guidelines have recommended that antibiotic prophylaxis (AMP) should be given only at premedication, except in selected cases. Conversely, in clinical practice, AMP is often unnecessarily prolonged after the surgical procedure. In this observational study, we evaluated the risk of surgical site infection (SSI) associated with the prolongation of AMP after clean and clean-contaminated surgery.

METHODS

All consecutive patients who underwent a surgical procedure were eligible. AMP was always administered before the surgical incision. Prolongation of AMP for the first 24 hours was allowed only in presence of at least one risk factor for SSI: an ASA score >2 or surgical procedure longer than the specific cutoff (as indicated by the NNIS--the National Nosocomial Infections Surveillance System). SSIs were evaluated during the hospital stay and after hospital discharge.

RESULTS

Three hundred fifty-eight patients were enrolled; 19 (5.3%) and 17 (6.5%) patients developed respectively intra-hospital and post hospital discharge SSIs. AMP prolongation for 24 hours in patients with at least one risk factor did not reduce the risk for intra-hospital SSI (OR 1.102; 95% CI: 0.336-3.612; P=0.873), while it increased the risk in patients without risk factors (OR: 8.99; 95% CI: 1.46-55.4; P=0.018). AMP longer than 24 hours raised the risk for intra-hospital and post hospital discharge SSI, regardless of the presence of risk factors (OR: 3.39; 95% CI 1.11-10.35; P=0.032 and OR: 5.39; 95% CI: 1.64-17.75; P=0.006, respectively.)

CONCLUSION

Postoperative AMP prolongation should be avoided.

Effects of different continuous positive airway pressure devices and periodic hyperinflations on respiratory function

OBJECTIVE

To compare the effect on respiratory function of different continuous positive airway pressure systems and periodic hyperinflations in patients with respiratory failure.

DESIGN

Prospective

SETTING

Hospital intensive care unit.

PATIENTS

Sixteen intubated patients (eight men and eight women, age 54 +/- 18 yrs, PaO2/FiO2 277 +/- 58 torr, positive end-expiratory pressure 6.2 +/- 2.0 cm H2O).

INTERVENTIONS

We evaluated continuous flow positive airway pressure systems with high or low flow plus a reservoir bag equipped with spring-loaded mechanical or underwater seal positive end-expiratory pressure valve and a continuous positive airway pressure by a Servo 300 C ventilator with or without periodic hyperinflations (three assisted breaths per minute with constant inspiratory pressure of 30 cm H2O over positive end-expiratory pressure).

MEASUREMENTS AND MAIN RESULTS

We measured the respiratory pattern, work of breathing, dyspnea sensation, end-expiratory lung volume, and gas exchange. We found the following: a) Work of breathing and gas exchange were comparable between continuous flow systems; b) the ventilator continuous positive airway pressure was not different compared with continuous flow systems; and c) continuous positive airway pressure with periodic hyperinflations reduced work of breathing (10.7 +/- 9.5 vs. 6.3 +/- 5.7 J/min, p <.05) and dyspnea sensation (1.6 +/- 1.2 vs. 1.1 +/- 0.8 cm, p <.05) increased end-expiratory lung volume (1.6 +/- 0.8 vs. 2.0 +/- 0.9 L, p <.05) and PaO2 (100 +/- 21 vs. 120 +/- 25 torr, p <.05) compared with ventilator continuous positive airway pressure.

CONCLUSIONS

The continuous flow positive airway pressure systems tested are equally efficient; a ventilator can provide satisfactory continuous positive airway pressure; and the use of periodic hyperinflations during continuous positive airway pressure can improve respiratory function and reduce the work of breathing.

Mesenteric and renal oxygen transport during hemorrhage and reperfusion: evaluation of optimal goals for resuscitation

BACKGROUND

Changes in flow to the gut and the kidney during hemorrhage and resuscitation contribute to organ dysfunction and outcome. We evaluated regional and splanchnic oxygen (O2) flow distribution and calculated oxygen supply distribution during hemorrhage and reperfusion and compared them with global measures.

METHODS

Seven anesthetized pigs were instrumented to evaluate global hemodynamics, visceral blood flow, and oxygen transport. Tonometric pH probes were positioned in the stomach and jejunum. Animals were bled to 45 mm Hg for 1 hour. Crystalloids and blood were infused during the following 2 hours to normalize blood pressure, heart rate, urine output, and hemo- globin.

RESULTS

During hemorrhage, mesenteric flow and O2 consumption were significantly decreased, whereas systemic consumption remained normal. Renal flow was reduced, but renal O2 consumption remained normal. After resuscitation, despite normal hemodynamics, neither systemic, mesenteric, nor renal O2 delivery returned to baseline. Lactate remained significantly increased. Arterial pH, base excess, and gastric and jejunal pH were all decreased.

CONCLUSION

During hemorrhage, the gut is more prone than other regions to O2 consumption supply dependency. After resuscitation, standard clinical parameters do not detect residual O2 debt. Lactate, arterial pH, base excess, and intramucosal gut pH are all markers of residual tissue hypoperfusion.

[Mechanical ventilation in acute respiratory distress syndrome. New Trends]

Adult Respiratory Distress Syndrome (ARDS) is characterized by an inflammatory process affecting endothelial and epithelial lung tissue, with occurrence of hypoxemia, bilateral X-ray infiltrates, in absence of cardiogenic edema. The introduction of Computerized Tomography brought some improvements in understanding the ARDS lung, leading to a pulmonary model made up of three zones: 1) normally inflated, 2) recruitable and 3) consolidated. It has now been well established that mechanical ventilation of ARDS lung presents some iatrogenic effects that may affect mortality. Several mechanisms are considered responsible of ventilator-associated lung injury (VALI): high inspired oxygen fraction, high inspiratory plateau pressure and large tidal volume, and intratidal collapse and reinflation of alveolar units. In these years, different ventilatory strategies in the treatment of ARDS patients have been suggested to decrease and to prevent VALI. The most important one seems to be the application of an appropriate value of tidal volume and positive end-expiratory pressure (PEEP). Several randomized studies, which compared low versus high tidal volumes, have recently been finished. Despite some differences, it seems that a ventilatory management limiting inspiratory plateau pressure to 35 cmH2O or lower may be useful to reduce VALI and mortality, also in association with a PEEP level sufficient to decrease the end-expiratory collapse. Another useful ventilatory tool for improving gas exchange and decreasing VALI in ARDS patients is likely the prone positioning, even if further studies are necessary to understand how this maneuver may really affect mortality. Another therapeutic instrument for improving oxygenation in ARDS patients is the inhalation of NO. Unfortunately, this pharmacological agent does not seem to affect the outcome of these patients.

[Positive end expiratory pressure in anesthesia]

It is well established that general anesthesia, with or without paralysis, causes profound changes in respiratory function. From a clinical point of view, the more important consequence of this impairment is a decreased efficiency of gas exchange, with a decreased blood oxygenation. The main reason of this respiratory embarrassment is the intraoperative occurrence of atelectasis, mainly in the dependent lung regions. The amount of atelectasis, computed through Computerized Tomography, correlates with the amount of intrapulmonary shunt; thus, alveolar collapse and ventilation/perfusion mismatching are considered the most important factors for poor respiratory function. This deterioration seems also to play a crucial role in obese patients, who have poorer respiratory function and gas exchange than normal subjects already in physiological conditions. Different ventilatory approaches have been tried to resolve and eventually prevent the anesthesia-induced atelectasis. In normal subjects, the sole application of positive end-expiratory pressure (PEEP) seems to be an useless tool for improving gas exchange, probably because of changes in hemodynamics functions. The only effective application of PEEP seems to be in association to an alveolar recruitment manoeuvre. As the anesthesia-induced atelectasis are also present in the postoperative period, this ventilatory approach may also be used to prevent this condition. In obese patients PEEP seems to have a major effectiveness than in normal subjects, with an improvement of lung volumes, respiratory mechanics, gas exchange and an occurrence of recruitment. However, further studies are necessary to define optimal value of PEEP and tidal volume for different types of patients.

Positive end-expiratory pressure improves respiratory function in obese but not in normal subjects during anesthesia and paralysis

BACKGROUND

Morbidly obese patients, during anesthesia and paralysis, experience more severe impairment of respiratory mechanics and gas exchange than normal subjects. The authors hypothesized that positive end-expiratory pressure (PEEP) induces different responses in normal subjects (n = 9; body mass index < 25 kg/m2) versus obese patients (n = 9; body mass index > 40 kg/m2).

METHODS

The authors measured lung volumes (helium technique), the elastances of the respiratory system, lung, and chest wall, the pressure-volume curves (occlusion technique and esophageal balloon), and the intraabdominal pressure (intrabladder catheter) at PEEP 0 and 10 cm H2O in paralyzed, anesthetized postoperative patients in the intensive care unit or operating room after abdominal surgery.

RESULTS

At PEEP 0 cm H2O, obese patients had lower lung volume (0.59 +/- 0.17 vs. 2.15 +/- 0.58 l [mean +/- SD], P < 0.01); higher elastances of the respiratory system (26.8 +/- 4.2 vs. 16.4 +/- 3.6 cm H2O/l, P < 0.01), lung (17.4 +/- 4.5 vs. 10.3 +/- 3.2 cm H2O/l, P < 0.01), and chest wall (9.4 +/- 3.0 vs. 6.1 +/- 1.4 cm H2O/l, P < 0.01); and higher intraabdominal pressure (18.8 +/-7.8 vs. 9.0 +/- 2.4 cm H2O, P < 0.01) than normal subjects. The arterial oxygen tension was significantly lower (110 +/- 30 vs. 218 +/- 47 mmHg, P < 0.01; inspired oxygen fraction = 50%), and the arterial carbon dioxide tension significantly higher (37.8 +/- 6.8 vs. 28.4 +/- 3.1, P < 0.01) in obese patients compared with normal subjects. Increasing PEEP to 10 cm H2O significantly reduced elastances of the respiratory system, lung, and chest wall in obese patients but not in normal subjects. The pressure-volume curves were shifted upward and to the left in obese patients but were unchanged in normal subjects. The oxygenation increased with PEEP in obese patients (from 110 +/-30 to 130 +/- 28 mmHg, P < 0.01) but was unchanged in normal subjects. The oxygenation changes were significantly correlated with alveolar recruitment (r = 0.81, P < 0.01).

CONCLUSIONS

During anesthesia and paralysis, PEEP improves respiratory function in morbidly obese patients but not in normal subjects.

[The sigh in ARDS (acute respiratory distress syndrome)]

We studied 10 consecutive, sedated and paralyzed patients with Acute Respiratory Distress Syndrome (ARDS). The entire study lasted 4 hours, divided in 3 periods: 2 hours of recommended ventilation [lung protective strategy, LPS, i.e., ventilation with low tidal volume (< 8 mL/kg), limiting the plateau at 35 cm H2O, together with high positive end-expiratory pressure (PEEP)], 1 hour of sigh (LPS with 3 consecutive sighs/min at 45 cm H2O plateau pressure), and 1 hour of LPS. Total minute ventilation, PEEP, FiO2 and mean airway pressure were kept constant. The introduction of sighs induced a consistent recruitment and PaO2 improvement, and a decrease in venous admixture and PaCO2. Interrupting sighs and resuming LPS led to a progressive derecruitment, and all the physiological variables returned to baseline. Derecruitment was higher in patients with higher PaCO2 and lower VA/Q ratio. We conclude that: 1) LPS alone does not provide full lung recruitment and best oxygenation in ARDS; 2) application of sigh may provide pressure enough to recruit and volume enough to prevent reabsorption atelectasis.

Sigh in acute respiratory distress syndrome

Mechanical ventilation with plateau pressure lower than 35 cm H2O and high positive end-expiratory pressure (PEEP) has been recommended as lung protective strategy. Ten patients with ARDS (five from pulmonary [p] and five from extrapulmonary [exp] origin), underwent 2 h of lung protective strategy, 1 h of lung protective strategy with three consecutive sighs/min at 45 cm H2O plateau pressure, and 1 h of lung protective strategy. Total minute ventilation, PEEP (14.0 +/- 2.2 cm H2O), inspiratory oxygen fraction, and mean airway pressure were kept constant. After 1 h of sigh we found that: (1) PaO2 increased (from 92.8 +/- 18.6 to 137.6 +/- 23.9 mm Hg, p < 0.01), venous admixture and PaCO2 decreased (from 38 +/- 12 to 28 +/- 14%, p < 0.01; and from 52.7 +/- 19.4 to 49.1 +/- 18.4 mm Hg, p < 0.05, respectively); (2) end-expiratory lung volume increased (from 1.49 +/- 0.58 to 1.91 +/- 0.67 L, p < 0.01), and was significantly correlated with the oxygenation (r = 0.82, p < 0.01) and lung elastance (r = 0.76, p < 0.01) improvement. Sigh was more effective in ARDSexp than in ARDSp. After 1 h of sigh interruption, all the physiologic variables returned to baseline. The derecruitment was correlated with PaCO2 (r = 0.86, p < 0.01). We conclude that: (1) lung protective strategy alone at the PEEP level used in this study may not provide full lung recruitment and best oxygenation; (2) application of sigh during lung protective strategy may improve recruitment and oxygenation.